System of central current-supply for private-line telephone-circuits.



SYSTEM OF CENTRAL CURRENT SUPPLY FDR PRIVATE LINE TELEPHONE CIRCUITS.

(Application Med Oct. 4, 1900) 2 Sheets-SheeI I.

(No Model.)

INVENTOR.

W! T NESSES ATTORNEY.

THE u'onms PETERS O0.. PHOTOLITHQ, WASHINGTON ay No. 669,901. Patented Mar. l2, I90I.

M. C. RURTY. SYSTEM OF CENTRAL CURRENT SUPPLY FOR PRIVATE LINE TELEPHONE CIRCUITS.

(Application filed Oct. 1, 1900) (No Model.) 2 Sheets-,Sheet 2.

Fig. 2.

WITNESSES INVENTOR.

I BY

y ATTORNEY.

THE mamas PETERS co. wuxflin'nod WASHINGTON, u c.

ilfinrmnn STATES PATENT OFFICE,

MALCOLM C. RORTY, OF DEDHAM, MASSACHUSETTS, ASSIGNOR TO THE AMERICAN BELL TELEPHONE COMPANY, OF BOSTON, MASSACHU- SETTS.

SYSTEM OF CENTRAL CURRENT-SUPPLY FOR PRIVATE-LINE TELEPHONE-CIRCUITS;

SPE IFI AT N forming part of Letters Patent No. 669,901, dated March 12, 1901.

Application filed October 4, 1900. Serial No. 32,028. (No model.) i

T0 on whom it may concern.-

Be it known that I, MALCOLM O. RORTY, residing at Dedham, in the county of Norfolk and State of Massachusetts, have invented certain Improvements in Systems of Central Current-Supply for Private-Line Telephone- Circuits, of which the following is a specification.

This invention concerns telephone-circuits and their operation, and more particularly relates to private telephone-circuits and to a system for enabling such private lines to participate in the advantages of the central-battery system.

A private telephone line or circuit is one with which two or more particular telephonestations are permanently associated, each such station being restricted to comm unication with the other stations of the same circuit and which does not constitute a member ofa telephone-exchange to be interconnected with other lines by means of a switchboard for the establishment of through communication with the telephones of such other lines. Prior to this invention the supply of signaling and transmitter currents to such private lines from centrally-placed sources has, so far as I am aware, not been attempted, and it has therefore uniformly been necessary to place at each station of such lines a local magneto-electric call-generator for the development of the currents required in the operation of call devices or signals and a local transmitter-battery for the production of the requisite telephone-transmitter current.

The object of this invention is to provide for private line-circuits the advantages of having their sources of current necessary for all purposes centralized without introducing the intermediation of a central-station switchboard and the intermediary switching and signaling operations of a central-station operator.

To this end the invention provides that the private line-circuit shall enter a central station and shall there normally and also while telephonic communication is going on be connected with a source of steady current, such as a battery, while a source of alternating current, such as is required for the operation of standard polarized bells, shall also be placed at the said central point and shall be associated with special apparatus responsive to the consecutive closing and opening of the main circuit at either operative station and thereupon acting to disconnect the main circuit temporarily from the source of steady current and to connect it with the source of alternating current for a brief but definite period of time, during which the call-bell at the station desired, and incidentally the bell at the calling-station also, may be operated and rung to give the call-signal. The circuit at the operative stations is arranged in the well-known plan generally adopted for central-battery exchange-circuits. The electromagnetic call-bell is placed in one continuation branch of the circuit, which also con tains a condenser, and the circuit is normally in connection with this branch. The condenser does not oppose the passage of the alternating ringing-currents, but maintains the circuit in a conductively incomplete condition, so that though the central source of steady current is normally connected no current can flow therefrom through said circuit. The station-telephones are in a sepa rate continuation branch of the circuit which is conductively continuous, so that when this branch is substituted for the former a shunt is established around the condenser, the main circuit is conductively closed, and steady current from the normally-connected source may flow therein. At each operative station there is means for producing such a closure of the main circuit, This may be a special circuitclosing switch; but I prefer to employ the usual hook-lever switch, serving when the line is unemployed as a telephone-supportand moving in adirection to close the circuit when the telephone is removed and to reopen the circuit when the same is replaced. The special appliances at the central station comprise a circuit-changer comprehending movable terminals of the main circuit transferable between fixed terminals of the steady and alternating sources of current respectively, so that when connection is established with the terminals of the steady-current source or battery, the main circuit being conductively closed by the action of the operative-station switch pursuant to the removal of the telephone, a steady current from said battery flows over the circuit to supply the telephone-transmitters thereof and also to furnish power for the source-transferring mechanism, while when this original connection is disestablished and the line-terminals are united to the terminals of the alternative source alternating call-currents traverse the main circuit and, acting through the condensers, operate the stationbells. The said circuit-changer is actuated by an electromagnet in a local circuit, this being controlled by a slow-acting relay also in a local circuit, and this in turn by a mainline relay associated with the normal battery connection in such manner as to be responsive to the movements of the operative-station switch. The operation of closing the circuit by one movement of said switch brings the said relays-into position for action, and the reverse motion of said switch produces such action and closes the circuit of the circuitchanger, which thereupon transfers the line from the source of steady current to the source of alternating current. After the lapse of suflicient time to transmit an effective ringing signal the slow-acting relay breaks the circuit of the actuating-magnet and the circuit-changer reestablishes the normal condition of the circuits.

In the drawings which accompany this specification, Figure 1 is a conventional diagram of a telephone-circuit containing the invention. Fig. 2 is a similar diagram of a similar circuit, illustrating a modified ar-' rangement which in some respects is an improvement. Fig. 3 illustrates the employment at the telephone-stations of a special switch having no other function than that of opening and closing the circuit, and Fig. 4 illustrates a sluggish or slow-acting relay suitable for use in a circuit embodying the invention.

Similar parts have similar letters and unmerals of reference in all of the figuresv L is a telephone-circuit, which may be a private-line circuit having main conductors ct 1), extending between operative telephonestations A and B and connecting with a central or intermediate station 0 by a loop L having, conductors d and e, leading from the main conductors CL and b, respectively. At each operative station is the usual polarized electromagnetic call-hell m, condenser c, telephone-transmitter M, receiver 25, inductioncoil I, and telephone-supporting switch 3. The bell and condenser are in series in a continuation branchoc of the main circuit, which normally constitutes the only electrical. connection at the station between the conductors of said circuitthatis, when the switch is in the position shown,with the telephone in place thereon. Under these conditions the circuit is conductively open or discontinuous in virtue of the presence of the condenser, which, however, forms practically no bar to the op eration of the bell by the alternating call-cu rrents when transmitted over theline. Another continuation branch 1 which I term the telephone branch, is also provided, and when the telephone tis removed from the switch the point at on conductor 7) is united to point 5 on conductor a through the transmitter M and the secondary winding of the inductioncoil 1, and the condenser being thus shunted the main circuit is conductively closed.

At the central station C, S is the source of steady current. S is the source of alternating or call current; Z, an impedance-coil or electromagnetic resistance; H, the elect romagnetic switch or circuit changer, and V and W are ordinary and slow-acting relays, respectively.

R is a main-line relay, and E is the earth connection, which, though shown in several places, may conveniently be one and the same.

The source S may conveniently be a primary or secondary battery, and the source S is by preference a magneto-electric generator of alternating or call current.

The electromagnetic circuit-changer H has an actuating-electromagnet r in a local circuit of the battery leading from one pole of said battery by conductors 18, 20, and 19, the front stopjand armature 7c of the slow-acting relay W, conductor 24, armature n and back stop 0 of relay V, conductor 25, coil of mag net r, and conductor 26 to earth E or the other battery-pole. This local circuit is normally open between the armature and frontstop contacts In andj of the relay W, and the actuating-magnet r of the circuit-changer H thus is unexcited. Consequently the armature-lever contactsfand g, forming the movable terminals of the conductors d e of the main-circuit loop L remain in their normal retracted position and in contact, respectively, with the back contact-stops b and 7, which form the fixed terminals of the battery S. The said batteryis thusin normal connection with the main circuit, conductor 1) of said circuit being united to the plus-pole thereof, by way of conductor 6, arl'nature and back contacts g and 7 of the circuit-changer H, conductor 15, magnet-coils of relay R, conductor 16, one winding of the inductive resistance Z and conductors 17 and 18, and main conductor a, similarly united to the minus-pole of the battery by loop-conductord,armature and backstop contactsf 8 of the circuit-changer H, conductor 14:, the second winding of the coil Z, and conductor 13. No current flows over the main circuit as long as the telephones tat the stations A and B remain on their respective switchhooks, notwithstanding the normal connection of the battery, as described above; but the said battery establishes a definite potential on the circuit, whereby a current is developed in one-half of the circuit when the telephone is removed from its switch atone station and throughout the circuit when the switches at both stations, relieved from the ecaeoi weight of the telephones, move into position-J to close the circuit, by bringing the switchlevers s intocontact with the points 2 and 3. The electromagnetic resistanceZptfers an opposition due to its resistance only to the passage of the battery-current; bu'twhen the 3 station transmitters arein operation the said coil opposes impedance to the voice-currents 1 which traverse thefmain line, and a loss of 3 such currents, through the loop. L is thus avoided. The main line relay R is connect-ed the'circuit of the conductors 18, 17, 16, i

and 15, leading from one pole of the battery S to the fixed terminal 7 of the circuit-changer H and is therefore in permanent association with the said battery, so thatit is connected with the main circuit L when the said circuit -changer is in its normal position, with its 1 membersg andf in contact with the points '1 through the transmitter and induction-coil by making ,contact with the point 2.

It is by means of theactioijrof the said line-relay R that the actuating-magnet r of the circuitchanger H is in due season excited, and such action is exerted through the relays V and? W, as will be presently described; but as thei operation of the said line-relay B is depend ent upon the current of the battery S the steady current of that battery, as may now bej seen, is utilized only as a transmitter-j supply, but also as furnishing the agency whereby either operative station may cause a ringing-current to traversethe line for the purpose of operating the bell at the other operative station.

The alternating-current or call generator S has its poles extended by conductors 31 to the forward contact-stops 9 10 of the circuit-changer H, so that the said stops are fixed terminalsof the said generator. Obviously when the said circuit-changer is actuated for the motion of its armatures by the excitation of its actuating-magnet its movable members will be separated from the normal contact with the fixed terminals of the battery and transferred to a new contact with the :lixed terminals of the generator S Obviously also this new contact will continue as long as the'excitation of the actuatingmagnet continues and will bediscontinued when such excitation ceases, and it follows that during the pendency of such connection the call-generator is contained in the circuit callrcurrents developed thereby will pas'sfover the main-circuit conductors in both directions and will operate the telephone-station bells. A p The ordinary relay V and theslow-acting ,relay W are serially connected in localcircuit of the source S, which may be traced by way of conductors l8 and 20, magnet-coil of relay W, conductor 21, exciting-coil of relay ,V, conductor 22, to the armature iof relay R, and when said armatureis excited to the front stop It and conductor 23 and thence to earth at E, and thereby tothe otherlbat'terypole by conductors l2 and 13. This local circuit is therefore controlled by the line-relay R. The relay V is of the ordinary type, acting promptly in the release of-its armature when its magnet having been excited is demagnetized. The relay WV, however, is a slow-acting relay and acts with considerable sluggishness in allowing its armature to fall away after its magnet-coil circuit is opened. Relays adapted for such sluggish action are now well known and may be arranged in several wa. \"s, all of which, however, depend upon increasing either their magnetic or mechanical inertia, or both. For example, thetime required for discharge may be 'made longer by using a long thin core, by usihgdiflferen tial helices, or by shunting the exciting-coils,

while sluggishness in the retractive move ment of the armature pursuant to discharge may be imparted by providing heavy and nearly-balanced moving parts or by providing the armature with a dash-pot attachment, and the contact between the local points may further be protracted by mounting one or both of them on a spring.

A sluggish or slow-acting relay,such as mentioned in the preceding paragraph, is illustrated in Fig. 4. It has a long thin magnetic core 40, supported at opposite ends by plates 41 and 42 of insulating material. A helix or coil 43, wound on core 40, connects at one end to conductor 21 and at its other end to conductor 20. A heavy nearly-balanced armature 44, mounted to move slowly in response to the excitation of the core and also in its reverse motion when such excitation ceases, is pivoted to a bracket 45,the down ward move ment of the heavier end of the armature nearest the end of core being limited by a stop 46. i

47 and 48 are two spring-contactsseparated by insulation 49 and mounted on plate 42. Lower spring-contact 48 has an arm50, which depends into the path of upward movement of the armature 44 when said armatureisattracted by the excitation of core 40. The

armature pressing upwardly against-arm 50 resses swin -contact 48 u )wardl against spring-contact 47, thereby closing the local circuit from conductor 19, which connects with contact 47 to conductor 24, which conne c ts with contact 48. The armature 44 be ing attracted by the core 40", the contact between thelocal spring-contacts47 and 48 is of the loop L of the main circuit L, and the prolonged for an instant after the circuit, in-

cluding the exciting-coil 43, is opened, and this prolongation comes about by the combined action of the long core, which is slow in parting with its magnetism, the weight and inertia of the armature which is slow in yielding to the retractive rorces on the disappearance of the attracted force, and the resiliency of the spring-contacts, which makes them slow in separating when the pressure existing on them by the armature when attracted is released.

The armatures n and It of the relays V and NV, with the back contact-stop 0 of the former and the front contact-stopj of the latter, are in the local circuit of the circuit-changeractnating magnet T, which circuit therefore can be closed for the excitation of said magnet and the consequent operation of the said circuit-changer to transfer the main circuit from the battery to the magneto generator only when the armature n and the armature it simultaneously rest on their respective back and front contacts 0 andj. This occurswhen the local circuit, including the exciting-coils of both relays, having been closed by the operation of the line-relay R, is opened by the falling back of armature tot the said linerelay R, for when the said circuit of the relays V and W is thus broken the armature 'n of relay V falls promptly to its back stop 0, while the armature is of the sluggish relay W delays its retraction and maintains its contact with the front stopj for a brief period of time, presently, however, falling away in turn to its back stop; but while the contact between armature 7c and jointj persists, the armature n resting on its back stop 0, the local circuit of the circuit-changer-actuating magnet is closed and may be thus traced: from the battery S by conductors 1S and 20, branch conductor l9, pointj, armature k, conductor 24, armature 72, point 0, and conductor 25, to said actuating-magnet and thence to the opposite pole of the battery by conductor26, earth connection E, and conductors 12 and 13. The actuating-magnetrisin this manner transiently excited and transfers the loop L and main circuit L to the call-generator for the brief interval of time during'which such excitement continues.

When the armature It falls away from its magnet-pole and parts from front stopj, the circuit of the actuating-magnet a" is broken and the circuit-changer H resumes its normal position, transferring the main circuit back from its transient or temporary connection with the alternating-current generator S? to its normal and more permanent one with the battery S.

In Fig. 2 is illustrated a modified arrangement of the local circuit of the circuitchanger-actuating magnet r and the slowacting relay controlling the same, which in some respects is regarded as being preferable. The relay V may by such modification be dispensed with, together with one pair of separable contacts, a single relay W taking the hook-switch, as usual.

place of the two relays V and W of Fig. 1. This is the only change of importance. The relay W has two exciting-coils, differentially wound and connected, as shown, and has considerable magnetic inertia, while its mechanical and contact inertia is provided by employing one or more of the expedients hereinbefore enumerated. Itis thus enabled to perform satisfactorily the functions of a slow-acting relay. The conductor 18 connects the battery S with one end of the rear coil to of the relay W and the front coil 10 connects at one end with the remaining end of coil to and at its other end with the front stop j of the armature is, which itself is electrically united with conductor 25 of the local circuit of the actuating-magnet r. A conductor 22 unites the point it between the coil-windings w 10 of relay W with the front stop it of relay R, and the armature of said relay connects by conductor 23 with the other pole'of the battery.

In Fig. 2 a third operating-station N in a bridge N is conventionally indicated, and it is to be understood that a number of stations may be so connected with the same private line. 1

Although ordinarily it will be more convenientin practice to employ the telephone-support switch in the operation of ringing the bell of any station of the main circuit from another, a special switch having no other function may be added when desired. Such an appliance is indicated in Fig. 3, where, in addition to the telephone-switch s, a switch or circuit-closing lever Q is shown, normally retracted by a spring q, but adapted when pressure is exerted on its handle to bring a point 32, carried by it,into contact with a fixed point The switch-bar is electrically u nited by conductor 34 with one main conductor a, and the fixed point by conductor 35 with the other main conductor b of the main circuit. Hence when the switch Q makes contact between the points 32 and 33 the main circuit will be closed.

In the operation of this system let it be supposed that station A of the circuit L wishes to communicate with station B. The initial operation is to remove the telephone from the When this is done, current flows from the source S through conductor 18 and 17, a winding of the impedancecoil Z, conductor 16, relay R, conductor 15, contacts 7 and g of circuit-changer H, loopconductor 6, main conductor b, the switch and telephone branch at station A, main conductor a, loop conductor d, circuit-changer contacts f and 8, conductor 14, the other winding of the coil Z, and to the opposite battery-pole by conductor 13. The impedance-coil is of low resistance, and the current flowing is therefore of suificient strength to excite the line-relay R. Referring to Fig. 1 as being a more obvious exemplification of the principles involved, the operation of relay R closes the circuit of the two relays V and W, which are both excited and operate by attractingtheir armatures; butthe armature ii of relay V separates from its back stop before the armature 7c of relay W can reach its front stop, the latter relay being sluggish in coming into action as well as in going out Hence the circuit of the actuating-magnet 0" of the changing device His not closed. The person sending the call at A must now pull down his telephone-hook for a moment to open the main circuit, and current thereupon ceases to flow, the excitement of relay R is discontinued,and the armature of said relay falls back, once more opening the local circuit which contains the excitingcoils of relays V and W. The armature of relay V falls back instantly; but the armature of the slow-acting relay W is retained in its forward position for a short time during which the circuit of the circuit-changeractuaiing magnet is closed. The said magnet thus becomes transientlyexcited and operates, transferring the main circuit from its normal connection with the battery S to one with the call-generator Siand thus sending a ringingcurrent from the said generator over the line. The hells at both of the stations consequently ringing, the call-signal is given at station B,while the person giving the call at A hearing his own bell may infer that the operation is proceeding properly. Of course the period of ringing is short; but it has been found sufficiently long to satisfactorily ring the bells. The attendant atthe callingstation A having heard his own bell ring may now permit his switch to again close the circuit through the telephone apparatus, and conversation may be exchanged. In the modified arrangement of Fig. 2 the operation is precisely the same up to the excitation of the line-relay B. When this relay attracts its armature, a circuit of the battery is closed through the rear coil to of the slow-acting diiferential relay W and the armature in thereof is attracted,closing a branch of the circuit through the front coil 10 the stop j and armature 7c, and the circuit-changer-actuating magnet 0. No appreciable current, however, flows through this branch, because it is shunted by the direct return connection established by the contacts of relayR between the middle point it of the differential relay and the ground or the other battery-pole. When, however, the relay R responds to the circuit-opening operation of the switch at station A and allows its armature to be retracted, the shunt is removed and current now flows through both coils w and w" of the differential relay and through the actuating-magnet 0", which at once transmits the call-current to line; but the action of the said two coils of the sluggish relay on the core thereof is neutralizing, and after the brief season required by the relay to overcome its own general inertia the armature It also falls back and the actuating-magnet circuit opens, the generator S as in the former case, being thereby disconnected and the battery S restored. It is evident that when the excitement of the actHating-magnet 7' has ceased and the movable members f and g of the circuit-changer have consequently restored connection between the line and battery S the line-relay R, and therefore the relays V and W, ale again operated. Thus when the stat-ions have finished the conversation and have replaced their telephones on their hooks the bells will again be rung. If there are several stations connected with the main circuit, any or all of the in may be called in the same manner, it being manifest that to call any particular one it is only necessary to operate the switch at the callingstation a number of times corresponding to the signal of the station desired.

Having now fully described the invention and its mode of operation, I claim-- 1. In a telephone system, the combination of a main circuit; an electric bell at a station thereof; a switch at a second station thereof capable of being placed in either of two positions and adapted to conductively close the said circuit at its own station in one, and to open the same in the other of said positions; an electromagnel ic circuit-changer having its actuating-magnet in a local circuit open normally and while the switch at the second station is in position to close the said main circuit, a source of steady on rreut, and a source of alternating or ringing current adapted for alternative connection with said main circuit by means of said circuit-changer, the former when the local circuit of said actuating-magnet is open and the latter when the same is closed, and means responsive to the circuitopening operation of the switch at said second station for transiently closing the local circuit of said actuating-magnet and for then reopening the same the said sources of current circuit-changer and means 'for operating the same, being all located at a third station; whereby the main circuit connection may be transferred from the said source of steady current to the source of ringing-current for a brief period of time to operate the bell at the first station whenever the switch at the second station after having been in its circuitclosing position is moved to its circuit-opening position; substantially as set forth.

2. In a telephone system the combination with a main circuit extending between two telephone-stations, and provided at each with two branches containing respectively an electromagnetic bell in series with a condenser, and telephone apparatus, and with atelephone-supporting switch adapted when the telephone is hung thereon to connect the said main circuit with its b'ell branch, and when the telephone is removed to transfer the main circuit to its telephone branch; of apparatus and circuits at a third station consisting of a source of steady current for transmitter supply; a source of alternating or ringing current; an electromagnetic circuit-changer controlling terminals of the said main circuit IIO and the said sources of current, and adapted to connect the said sources alternatively with said main circuit; and means controlled by the said switches at the telephone-stations for controlling the said electromagnetic circuit-changer, and for causing the same to establish a transient connection between the main circuit and ringing-current-source terminals whenever the said telephone-switches or either of them after having united the main circuit and telephone branch shall be moved to transfer said main circuit to its bell and condenser branch; and to maintain connection between the said loop and steady-current-source terminals, at all other times; substantially as and for the purposes set forth.

3. In combination with aprivatetelephoneline circuit extending between two operative stations; a central or third station connected also therewith; a battery furnishing steady current normally connected with said circuit, and a generator furnishing an alternating signaling-current normally disconnected from said circuit at said central station; a callbell responsive to said signaling-current in a conductively open continuation branch, and a telephone in a conductively complete continuation branch of said main circuit, at each operative station; and means for enabling either operative station to transfer the main circuit transiently from the battery to the call'current generator at the central station and to thereby ring the bell at the other operative station, said means consisting of a switch at each operative station adapted to determine the flow of current in the said main circuit by transferring the same from either to the other of the said continuation branches thereof, and at the central station a circuitchanger actuated by an electromagnet in a local circuit and comprising movable terminals of said main circuit and fixed terminals of the battery and call-current generator respectively, a relay in circuit with the normal battery connection responsive to the movements of the switches at either of the said operative stations, and circuit controlling devices actuated by said relay, and controlling the local circuit of the said circuitchanger-actuating magnet to excite the said magnet for a brief period of time; substantially as described.

4. A central-battery private telephone-line system comprising the following circuits and instrumentalities in combination; a main private-line circuit extending between a plurality of operative telephone-stations, and entering a central station; a battery. at said central station normally connected with said main circuit; a bell and condenser branch in normal connection with said main circuit, a normally open telephone branch shunting the said condenser, and a switch actuated by the removal and replacement of the station-telephone to transfer the main circuit from the condenser branch to the telephone branch and vice versa, and thereby close and Open said circuit as respects the current of said battery, said parts located at each operative station; an alternating-current generator organized to develop ringing-current adapted to operate the telephone-station bells thro ugh their respective condensers, an electromagnetic circuit-changer adapted to transfer the said circuit from the battery to the call-gentwo subscribing witnesses, this 2d day of O0- tober, 1900.

MALCOLM O. RORTY.

Witnesses:

,GEO. WILLIS PIERCE,

J OSEPH A. GATELY. 

